Mobile hydraulic hammer with hammer stroke control



19% N. L. PETERSON ETAL 3,381,764

MOBILE HYDRAULIC HAMMER WITH HAMMER STROKE CONTROL Filed Oct. 15, 1966 IN VEN TORIS NORMAN L. PETERSON y ROBERT F. LEDER A M/M M, a ,1 wuf ATTORNEYS United States Patent 3,381,764 MOBILE HYDRAULIC HAMMER WITH HAMMER STROKE CONTROL Norman L. Peterson, Wauwatosa, and Robert F. Leder,

Milwaukee, Wis., assignors to Rex Chainbelt Inc., Milwaukee, Wis., a corporation of Wisconsin Filed Oct. 13, 1966, Ser. No. 586,536 5 Claims. (Cl. 173115) This invention relates to improvements in mobile hydraulic hammers and specifically to an arrangement for precisely setting the hammer drop height so that the impact of the hammer can be easily varied to suit any particular job.

Mobile hydraulic hammers are useful tools in various demolition and tamping work, such as breaking concrete, cutting asphalt, scoring pavement, tamping back fill, tamping slopes, piercing frost, and back filling. Such hammers commonly have an impact tool mounted for free fall or dropping under the force of gravity and a hydraulic motor for raising the tool. The height to which the tool is raised determines the impact force that the tool applies in its dropping. It is, of course, very desirable to allow an operator to select the drop height of the hammer as quickly, easily and efficiently as possible.

This invention provides an arrangement which allows an operator of a mobile hydraulic hammer to set the precise tool impact that the job calls for, i.e., to select a drop height of the hammer from one to ten feet by merely turning a dial to provide instant, effortless and infinite control of the hammer impact. The dial the operator turns is a variable resistance connected in an electrical timing circuit which in turn controls a solenoid dump valve in a hydraulic circuit for raising the tool. Hydraulic fluid under pressure raises the tool at a constant rate so that the elapsed time the tool is being raised determines the height to which it is raised. Near the bottom of the impact stroke of the tool the timing device is actuated and the tool is raised after impact for a predetermined period of time at the end of which the dump valve is open allowing the tool to drop and the hammer to drop to impact the pavement. Thus an operator can vary the impact on breaking surfaces of ditferent thickness and strengths or when moving over service lines, etc. The timing control is a transistorized system with no moving parts except for a single manual control of the resistance of the timing circuit.

Other features of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawing, which disclose by way of example the principle of the invention and the best mode which has been contemplated of applying that principle.

In the drawing:

FIG. 1 is a somewhat schematic front elevation view of the mobile hydraulic hammer incorporating the stroke control of this invention; and

FIG. 2 is a schematic diagram of the hydraulic and electrical circuit which allows the hammer action control.

In the drawing, FIG. 1 is a front elevation view of a vehicle having a weighted impact tool 12 for hydraulic hammering purposes such as breaking pavement and the like. The operation of the vehicle and its hydraulic hammering tool is described in more detail in US. Patent 3,225,842 assigned to the assignee of this invention.

The vehicle has a hydraulic circuit 14 for raising the tool at a substantially constant rate. This hydraulic circuit includes a hydraulic reservoir 16 with an inlet line 18 to a hydraulic pump 20. The outlet from hydraulic pump 20 goes through outlet line 22 to a three-way valve 24. The three-way valve has an outlet 26 for return to the reservoir, and an outlet 28 leading into a T connection 30. In normal operation the valve 24 allows the pressure of the pump to go through outlet 28 to T connection 30.

3,381,764 Patented May 7, 1968 "ice At that point the pressurized hydraulic circuit has two branches; one through line 32 to a hydraulic cylinder 34 which is the hydraulic lift cylinder of the mobile hydraulic hammer. The other line 36 goes to a solenoid controlled dump valve 38 having its outlet 40 leading back into reservoir 16. A solenoid 42 controls the opening of dump valve 38. A piston 44 is within cylinder 34 and with pump pressure applied to T connection 30 and dump valve 38 closed the pressure will be applied underneath piston 44 to raise the piston and its piston rod 46 against the weight applied thereto by the machine raising the piston at a constant rate to a predetermined height at which the dump valve 38 is opened by energizing solenoid 42 dumping the hydraulic pressure from below the piston 34 through hydraulic lines 30, 36 and 40 back to the reservoir. At this time the weight bias applied to the top of the piston rod 46 will cause the rod and percussive tool to move downwardly. The height that the piston 44 is raised determines the impact of the stroke. Hence, it is very desirable to accurately control the height to which the piston within the hydraulic cylinder is raised.

This invention allows the stroke of the hydraulic cylinder to be easily and accurately set by setting an electronic timing circuit 50. This electronic timing circuit controls the time that the hydraulic pressure of the pump 20 is applied to the underside of the piston 44. After a predetermined period of time has elapsed, and this is set by a variable resistance within the timing circuit 50, the solenoid 42 is energized dumping the pressure and starting the downstroke, thus determining the impact of the tool 12.

The timing circuit 50 is energized from the negative side of the vehicle battery 52 and controlled through switch 54. A further control for starting and stopping of the timing circuit is a limit switch 56 which is normally closed, but is opened near the bottom of the stroke of the piston 44 by switch actuator 58 which is a bracket secured to piston rod 46. The timing circuit is an RC circuit including capacitor 60 and variable resistance 62. The variable resistance may be set by an operator controlled dial of the vehicle to, in effect, dial the stroke of the hammer. The circuit also includes transistor 64, SC R66 and a power transistor 68 as well as a diode 70 connected as shown in FIG. 2 to control energization of solenoid 42 after a predetermined length of time.

The operation of the electronic timing circuit 50 is as follows: When switches 54 and 56 are closed thereby connecting battery 52 to the timing circuit, capacitor 60 be gins charging at a rate dependent upon the values of capacitance 60 and resistance 62. By varying the resistance of resistor 62, the rate at which the voltage across capacitor 60 increases may be controlled. When the voltage at the junction of capacitor 60 and resistance 62 reaches the threshold level of unijunction transistor 64, the latter transistor is energized thereby applying a positive pulse to the input gate terminal of SCR 66. The silicon controlled rectifier 66 is rendered conductive by the gating pulse from transistor 64. Current flowing through resistor 72 lowers the potential of the base terminal of transistor 68 to turn on and provide a connection between solenoid 42 and battery 52.

As long as transistor 68 remains conducting, solenoid 42 is energized and dump valve 38 is open. The action of SCR 66 in combination with resistor 72 maintains transistor 68 in a conducting state until either switch 56 or switch 54 is opened causing 'SCR 66 to turn off.

In the overall operation with limit switch 56 closed by the downstroke of piston 44 the timing circuit will energize solenoid 42 but only after a predetermined delay and until this time hydraulic pressure from pump 20 to threeway valve 24 and T30 raises the piston 44. However, after the RC circuit discharges, solenoid 42 is energized opening dump valve 38, dumping the pressure from below piston 44 and allowing the piston to descend rapidly for the stroke of the hydraulic hammer. The amount of time before the solenoid 42 is energized dumping the pressure to start the impact stroke will determine the height to which the piston 44- is raised since the rate of rise of the piston 44 and tool is constant. When solenoid 42 is energized opening dump valve 38 the piston starts its descent and continues its descent with the solenoid 42 energized until switch actuator 58 opens normally closed limit switch 56. At this time the solenoid 42 is -de-energized, dump valve 38 automatically closes and pressure from pump 20 is then again applied through branch line 32 to the bottom of cylinder 34 to start raising the piStOIl 44. On start of the piston upstroke the switch 56 will again return to its normally closed position restarting the t ming circuit.

It can thus be seen that by an operator merely controlling a dial setting variable resistance 62 the hammer stroke for the precise job height that the job requires can be set quickly, easily, etiortlessly, by the operator for providing an infinite control of the hammer impact and stroke when breaking surfaces of various thicknesses and strength.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

'1. In a vehicle having a weighted impact tool for breaking concrete pavement and the like, a hydraulic circuit having a motor for raising said tool at a substantially constant rate and a dump valve which when opened allows the tool to drop by gravity, a variable resistance controlled electrically charged timing means which is started as the tool passes a given point near the point at which the tool impacts the pavement, said timing means being connected to said dump valve to open the same after a preselected elapsed time after starting, and manual means for varying said resistance whereby the elapsed time, the height to which the tool is raised and the force of the dropped impact of the tool is varied.

-2. In a vehicle having a weighted impact tool for breaking concrete pavement and the like, a hydraulic system including a motor for raising said tool at a substantially constant rate and a dump valve which when opened allows the tool to drop by gravity, the improvements comprising a variable resistance controlled electrically charged timing means, a switch operated by the tool at a given point near the point at which the tool impacts the pavement, said timing means being connected to said switch and to said dump valve to close the latter for a preselected elapsed time after operation of said switch, and manual means for varying said resistance whereby the elapsed time, the height to which the tool is raised and the force of the dropped impact of the tool is varied.

3. In a vehicle having a weighted impact tool as in claim 2 wherein the switch operated by the tool is a normally closed limit switch operated by a switch actuator movable with the tool.

4. In a vehicle having a weighted impact tool as in claim 3 wherein the dump valve is a solenoid controlled valve.

5. In a vehicle having a weighted impact tool as in claim 4 wherein the timing means includes a capacitor electrically connected to the variable resistance and semiconductor electronic components to control energization of the solenoid a preset period of time after the limit switch is closed.

References Cited UNITED STATES PATENTS 2,619,072 11/1952 Clarke et al 173--ll5 X 2,672,331 3/1954 Cornett 1731l5 X 2,862,475 12/1958 Kinsman .h 9l--39 X ERNEST R. PURSER, Primary Examiner. 

1. IN A VEHICLE HAVING A WEIGHTED IMPACT TOOL FOR BREAKING CONCRETE PAVEMENT AND THE LIKE, A HYDRAULIC CIRCUIT HAVING A MOTOR FOR RAISING SAID TOOL AT A SUBSTANTIALLY CONSTANT RATE AND A DUMP VALVE WHICH WHEN OPENED ALLOWS THE TOOL TO DROP BY GRAVITY, A VARIABLE RESISTANCE CONTROLLED ELECTRICALLY CHARGED TIMING MEANS WHICH IS STARTED AS THE TOOL PASSES A GIVEN POINT NEAR THE POINT AT WHICH THE TOOL IMPACTS THE PAVEMENT, SAID TIMING MEANS BEING CONNECTED TO SAID DUMP VALVE TO OPEN THE SAME AFTER A PRESELECTED ELAPSED TIME AFTER STARTING, AND MANUAL MEANS FOR VARYING SAID RESISTANCE WHEREBY THE ELAPSED TIME, THE HEIGHT TO WHICH THE TOOL IS RAISED AND THE FORCE OF THE DROPPED IMPACT OF THE TOOL IS VARIED. 